Java Picture Processor: PGM files and Arrays

I need some Java help, I've sought out help from my professor with no luck. We're doing a picture processing program in Java. Basic functions are flip vertical and horizontal, invert and rotate. They've written most of the code, which can be found here: http://www.cs.colostate.edu/~cs160/pub/Pic.java

Basically I don't know how to get started. They have a comment in each method (eg negate) // YOUR CODE GOES HERE. I'm pretty good on the logic/understanding part of the java program but am struggling with the code part. I see that there is a private method that handles the image into an array, I'm thinking I probably need to use that. When I've tried it gives me an veriable scope error.